Abstract
This paper discusses over the air (OTA) testing for multiple input multiple output (MIMO) capable terminals with emphasis on modeling bidirectional spatial channel models in multiprobe anechoic chamber (MPAC) setups. In the literature, work on this topic has been mainly focused on how to emulate downlink channel models, whereas uplink channel is often modeled as free space line-of-sight channel without fading. Modeling realistic bidirectional (i.e., both uplink and downlink) propagation environments is essential to evaluate any bidirectional communication systems. There have been works stressing the importance of emulating full bidirectional channel and proposing possible directions to implement uplink channels in the literature. Nevertheless, there is no currently published work reporting an experimental validation of such concepts. In this paper, a general framework to emulate bidirectional channels for time division duplexing (TDD) and frequency division duplexing (FDD) communication systems is proposed. The proposed technique works for MPAC setups with arbitrary uplink and downlink probe configurations, that is, possibly different probe configurations (e.g., number of probes or their configurations) in the uplink and downlink. The simulation results are further supported by measurements in a practical MPAC setup. The proposed algorithm is shown to be a valid method to emulate bidirectional spatial channel models.
Highlights
Multiple-input multiple-output (MIMO) systems have demonstrated their capabilities to improve system capacity and link reliability in rich multipath environments [1]
Based on the measurement results and the results reported in the literature, it can be summarized that (i) large and small scale parameters in uplink and downlink channels are highly correlated both for the time division duplexing (TDD) and frequency division duplexing (FDD) systems, and large and small scale parameters used in the downlink channels can be adopted for the uplink channels directly; (ii) fading coefficients for the uplink and downlink are fully correlated in TDD systems, while fading coefficients of downlink and uplink might be correlated in FDD systems, depending on the frequency separation, and the channel frequency correlation function (FCF)
This paper addresses techniques to emulate bidirectional channel models in multiprobe anechoic chamber (MPAC) setups
Summary
Multiple-input multiple-output (MIMO) systems have demonstrated their capabilities to improve system capacity and link reliability in rich multipath environments [1]. Several different OTA systems have been proposed to evaluate MIMO capable terminals, for example, the two stage systems (with the conducted/radiated option) [4, 5], reverberation chamber based systems (with/without a radio channel emulator) [6, 7], and multiprobe anechoic chamber (MPAC) systems (with two-dimensional (2D)/3D probe configurations) [8, 9]. The uplink channel state information can be critical for downlink performance in some closed loop communication systems with adaptive modulation, coding, and MIMO transmission modes. (iii) Several multiprobe anechoic chamber setups, capable of emulating realistic bidirectional channels, are proposed and evaluated. To the best of the authors knowledge, it is the first time that bidirectional channel models have been emulated in a practical MPAC setup for MIMO OTA testing
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